The conventional A/D converter, which has been used for indicating in digital form analog signals obtained by measurements, has chiefly carried out a continuous A/D conversion. Thus it is necessary to provide a separate holding mechanism in order to hold the values of the signals in digital form and the electric circuit is made complicated, and apparatus becomes expensive. Furthermore, such a conventional A/D convertor is large-sized and has not been miniaturized because of the shape, specification, power supply and the like of an A/D converting element thereof.